Magnetic (or magneto-resistive) random access memory (MRAM) is a non-volatile memory technology that shows considerable promise for long-term data storage. Performing read and write operations on MRAM devices is much faster than performing read and write operations on conventional memory devices such as DRAM and Flash and order of magnitude faster than long-term storage device such as hard drives. In particular, future generation MRAM devices, such as “Spin Torque,” “Thermal Select,” “Thermally-Assisted Spin Torque,” operate at low voltages, and have low power consumption. In MRAM devices, the information is no longer stored by electrical charges, as in semiconductor memories, but by two opposite directions of the magnetization vectors in a small magnetic structure.
Conventionally, the basic MRAM cell is the so-called magnetic tunnel junction (MTJ) which consists of multiple ferromagnetic layers sandwiching at least one non-magnetic layer. Information is stored as directions of magnetization vectors in the magnetic layers. The magnetization of one of the layers, acting as a reference layer, is fixed or pinned and kept rigid in one given direction. The other layer, acting as the storage layer is free to switch between the same and opposite directions that are called parallel and anti-parallel states, respectively. The corresponding logic state (“0” or “1”) of the memory is hence defined by its resistance state (low or high).
The change in conductance for these two magnetic states is described as a magneto-resistance. Accordingly, a detection of change in resistance allows an MRAM device to provide information stored in the magnetic memory element. The difference between the maximum (anti-parallel; RAP) and minimum (parallel; RP) resistance values, divided by the minimum resistance is known as the tunneling magnetoresistance ratio (TMR) of the magnetic tunnel junction (MTJ) and is defined as (RAP−RP)/RP. To achieve high density and small size for future generations of MRAM, it is also important to develop deposition tool configurations for the fabrication of magnetic tunnel junction (MTJ) devices characterized by high tunneling magnetoresistance ratios (e.g.: TMR>100%), very low resistance-area values (e.g.: RA<10 Ω-μm2) and high breakdown voltage (e.g.: VBD˜0.6 V) for current-induced magnetization switching (CIMS).
MTJ stacking elements (magnetic and non-magnetic layers), including the tunnel barrier layers, are conventionally fabricated using sputtering deposition systems, such as Physical Vapor deposition (PVD) systems or Ion Beam Deposition (IBD) systems without vacuum break. Physical Vapor deposition (PVD), as well Ion Beam Deposition (IBD), can deposit a wide variety of materials at very low pressure, providing, for example, layers with high crystallinity. Although Atomic Layer Deposition (ALD) does not have such a flexibility, it is capable of depositing very smooth and uniform materials layers, very special requirements needed for the tunnel barrier layer in MTJ devices. Effectively, the resistance-area (RA) product of an MTJ device is an exponential function of the thickness of the tunnel barrier layer. Any deviation in the thickness uniformity of such tunnel barrier layer will have a critical impact on the reliability and performance of the MTJ device.
Another aspect that can have a critical impact on the performance of an MTJ device is the transfer process of a substrate between two deposition chambers. The interfaces of the deposited thin films can be affected when the deposition of a next thin film layer is performed in another deposition chamber than the last deposited layer. Performing the deposition of the critical layers such as the tunnel barrier in the same chamber as the bottom and top layers interfacing directly with it is important in avoiding degradation of the corresponding interfaces, which can lead to high quality tunnel barrier needed for high performance MTJ devices.
For these and other reasons, there is a need for the present invention.